I. Field
The present disclosure relates generally to electronics, and more specifically to power amplifiers.
II. Background
A wireless device (e.g., a cellular phone or a smartphone) in a wireless communication system may transmit and receive data for two-way communication. The wireless device may include a transmitter for data transmission and a receiver for data reception. For data transmission, the transmitter may modulate a radio frequency (RF) carrier signal with data to obtain a modulated RF signal, amplify the modulated RF signal to obtain an amplified RF signal having the proper output power level, and transmit the amplified RF signal via an antenna to a base station. For data reception, the receiver may obtain a received RF signal via the antenna and may amplify and process the received RF signal to recover data sent by the base station.
A wireless device typically includes a power amplifier (PA) to receive the RF signal modulated as desired for a given communication protocol and amplify this signal for transmission using an antenna. Typically, a PA can amplify both current and voltage of an incoming signal to provide the signal at a desired level. In an amplifier stage of the PA, if a phase shift through the stage is a function of the amplitude of the input signal, then that amplifier has a phase distortion, sometimes referred to as amplitude modulation-to-phase modulation (AM-to-PM) distortion. AM-to-PM distortion is a nonlinear process which degrades the amplifier's overall linearity.
In PAs formed using a complementary metal oxide semiconductor (CMOS) process, AM-to-PM distortion can cause a significant linearity problem. There are basically two sources in a CMOS PA contributing to the AM-to-PM distortion. One is the nonlinear gate capacitance of the common-source stage (CGS). Another is the nonlinear gate capacitance of the common-gate stage (CGD).